The present invention relates to a roll-up cover system, particularly to ventilate and adjust the temperature of horticultural greenhouses, and a horticultural greenhouse fitted with this cover system.
In temperate climate regions, greenhouses are an essential means for growing certain varieties of plants, fruits or vegetables. Thus, large farming estates are frequently equipped with several tens of horticultural greenhouses that protect the species grown from the cold, these greenhouses possibly being approximately one hundred meters long and approximately ten meters wide.
In order to adjust the temperature of the greenhouse that is necessary for the growth of the species grown, many greenhouses said to have “removable covers” are equipped with opening leaves that enable them to be ventilated when the temperature becomes too high due to the sun.
As an example, FIG. 1 schematically represents a model of a greenhouse 1 spread out comprising a frame or structure produced by assembling jambs 2, cross-pieces 3 and stringers 4, covered with a tarpaulin 5 made of transparent plastic, the vertical walls of the greenhouse being formed by a rigid or semi-rigid material fixed to the jambs. The tarpaulin 5 can be of the single-membrane type or of the double-membrane type, the double-membrane tarpaulins being inflatable and providing better heat insulation and resistance to the wind than single-membrane tarpaulins.
The greenhouse 1 has two openings, on each of its large sides, fitted with sorts of electric “screens”, made up of tarpaulins 6, 6′ wound onto shafts 7, 7′. The shafts 7, 7′ are driven by an electrical motor 8 through two universal joints 9, 9′. The motor 8 is itself controlled by a temperature adjustment system (not represented) that rolls up or unwinds the tarpaulins 6, 6′ according to the temperature in the greenhouse.
This type of greenhouse with automatic adjustment is inconvenient in that it requires at least two motors per greenhouse. Equipping a farm comprising many greenhouses of this type therefore requires purchasing and maintaining a substantial number of motors and the installation of a complex network of cables to distribute electricity.
There are also known models of greenhouses having motorised opening leaves arranged on the roof, that can be driven by a single motor. However, these opening leaves require a complex system of racks to unwind or roll up tarpaulins in a substantially horizontal plane.
Generally speaking, the roll-up tarpaulins of the opening leaves of greenhouses, whether they are arranged on the walls or on the roofs of the greenhouses, are inconvenient in that they are limp and little resistant to the wind, while the fixed tarpaulin covering the rest of a greenhouse can be chosen to be of the double-membrane inflatable type.
Another inconvenience of the known roll-up cover systems is that they require at least one motor per greenhouse, due to the mechanical losses by friction occurring in the transmission elements such as the universal joints and the racks.
The document DE9103345 describes a greenhouse fitted with a double-membrane tarpaulin [3, 4] in which the winding and unwinding of the tarpaulin is carried out by an automatic winder made up of two electric carriages [8, 9] mounted onto rollers [23] that run on guide rails [22]. These winding and unwinding carriages are secured to a winding cylinder [21] through a cylinder motor [19] of the blind motor type, equipped with a motor brake. The inflatable tarpaulin is linked to the output of a pressure generator [15, 16] through orifices [17]. The pressure in the tarpaulin is adjusted according to the climatic conditions to provide more or less heat insulation. The tarpaulin is inflated when the limit stop position is reached so as to create a heat insulation space [5]. In addition to the winding and unwinding carriages, this cover system according to the prior art is equipped with a return motion system comprising a cord [25] and a counterweight [26] that pull the carriages [8, 9] in an unwinding direction. It can also be seen in FIG. 2 of this document that the position of the tarpaulin is such that the unwinding is done in the direction of the low part of the inclined plane on which the tarpaulin rests, such that three means are involved in the unwinding of the tarpaulin: firstly the automatic winders or motorised carriages [8, 9], secondly the counterweights [26] attached to the carriages by the cords [25], and finally gravity itself, due to the arrangement of the tarpaulin that has just been mentioned. This document therefore describes a motorised cover system that is conventional in itself, of substantial complexity and a considerable cost price, in which the tarpaulin is a double-membrane inflatable tarpaulin instead of being a single-membrane tarpaulin.